Fixed the hinge loss equation

[guydav]

Fixed a small mistake in the hinge loss equation in 11-2 -- the subtraction of the offending example's energy was outside of the max operator, where it should be inside -- see the table provided later in 11.2, or slide 19 here: https://cs.nyu.edu/~yann/talks/lecun-20041200-ebm-whistler.pdf

[Atcold]

This is great. It would be even better if we replace \max(0, …) with (…)^+.
Would you be able to do that? Otherwise, I can merge this update.

[guydav]

@Atcold sure thing, see the latest commit.

[Atcold]

Awesome, thanks!